Tumors from MMTV-Wnt1/MMTV-Neu mice exhibit morphologic characteristics of Wnt1-induced tumors, despite expression of the Neu transgene. (A) Histological appearance of the tumors from (a) MMTV-Neu, (b) MMTV-Wnt1, and (c, d) MMTV-Wnt1/MMTV-Neu mice. Note solid morphology and scant stroma in the tumor from the MMTV-Neu mouse, in contrast with branched ductular architecture and dense stroma of the tumors from MMTV-Wnt1 and bitransgenic mice. (B) Immunohistochemistry on the consecutive sections of the tumor from a bitransgenic mouse with the following mammary lineage markers: (a) anti-smooth muscle actin (SMA), (b) anti-keratin 8 (TROMA), (c) anti-keratin 6, and (d) anti-Her2/Neu marker Ab3, was performed as described in Methods. The Her2/Neu marker is expressed in a subpopulation of cells similar to the one positive for keratin 8. (C) Detection of Neu RNA in mammary glands and tumors. RT-PCR for the rat Neu on the total RNA samples from the MMTV-Neu mouse mammary gland (MG) and tumor (MT), MMTV-Wnt1 mouse mammary tumor (MT), and MMTV-Wnt1/MMTV-Neu mouse mammary tumor (MT) and gland (MG).